Turbine outlet ducting



Feb. 12, 1957 P. J. FLETCHER I TURBINE OUTLET DUCTING 4 Sheets-Sheet 1 Filed Harsh l, 1954 FIG! ttorn Tull Feb. 12, 1957 "P. J. FLETCHER 2,781,057-

TURBINE OUTLET DUCTING Filed March 1, 1954 4 Sheets-Sheet 2 velgfgr P. J. FLETCHER. 2,781,057 TURBINEOUTLET DUC'IIING Feb. 12, 1957 4 Sheets-Sheet 3 Filed March 1, 1954 I nlar V I B y Feb. 12, 1957 Filed March 1, 1954 P. J. FLETCHER TURBINE OUTLET DUCTING 4 Sheets-Sheet 4 mrney United States atent 2,781,057 TURBINE OUTLET DUCTING Philip John Fletcher, Cove, Farnborough, England, as-

signor to Power Jets (Research and Development) Limited, London, England, a British company Ducting for leading the exhaust gases from one end of a steam, gas, or like turbine in a direction other than axially, and around the turbine so as to leave the turbine rotor bearing exposed has hitherto been in the form of a volute immediately around the outlet, and this volute has usually also provided for diflusion.

The object of the present invention is to reduceconsiderably the loss of head which is experienced with the aforesaid type of outlet ducting andfurthermore to do so while keeping the axial length occupied by the outlet reasonably short and leaving the bearing completely accessible.

The invention consists in a form of a duct unit for fluid, affording diffusion and also 'elfecting transition from an annular ditiuser duct, by way of a toroidal duct disposed around the difiuser axis, to a pipe extending transversely to the diifuser axis. With the object of avoiding losses due to whirling around the axis of the toroid which would be set up by introducing the gases into this duct unsymmetrically, and in particular tangentially, the primary feature of the invention is that an annular difluser passage continuing axially from the turbine outlet discharges directly or indirectly centrally into the toroidal duct along a radius of the cross section of the toroidal duct. Furthermore the toroidal duct is of progressively varying cross-section, such that it is non-(infusing. V V v The toroidal duct merges into a pipe extending usually radially away from it; the gases enter this toroidal duct around substantially its Whole circumference and accordingly the gases flow towards the pipe in two streams flowing in opposite directions from a point on the. toroidal outlet which is diametrically opposite the pipe, the streams being of progressively increasing volume so thatthe cross sectional area of the toroid accordingly progressively increases to accommodate this increase of volume but without diflusion. In order to provide suflicient length of path for the gases between a turbine and the annular entry into the toroidal duct to prevent disturbances due to the peculiar nature of the flow in this duct from affecting the turbine, it is an important feature of the invention to provide, between the axially extending diffuser and the annular inlet to the toroidal duct, an annular non-diifusing connection having the section of a substantially 180 pipe bend. There may be a further straight diffuser connecting the pipe bend member to the toroidal duct and enveloping the first diffuser, so that a considerable length and small angle of diffuser is obtained with minimum axial length. Preferably, according to an important feature of the invention, the member afiord-ing the 180 bend has a slight progressive decrease of crosssectional area, the whole of the diffusion being afiorded by the one or two straight annular diffusers and no diffusion taking place where there is any change of direction of flow.

One particular form of construction of duct according to the invention, suitable for attaching to the annular 2,731,057 Patented Feb. 12, 1957 2 outlet of an axial flow turbine, is shown in the accompanying drawings, of which: ,7

Figure 1 is a view in section on the axisof the difiuser; Figure 2 is a corresponding view in semi-perspective; Figure 3 is a view looking on Figure 1 in the direction of arrow III; and Figure 4 is a sectional viewlooking on Figure l in the direction of arrowlV. v v 1 in this construction a straight annular diffuser a can be mounted to extend from the outlet of a turbine is made up of inner and outer walls' land Zflahges at 111 and 2 1 for attachment to the. turbine. The walls and 2 are continued by tw'ofannular troughs fi and which members together define e bend b forming a continuation of the gas path from the difius'er andhav; ing a width decreasing progressively outwardly from the axis of the unit in such a manner that the cross-sectional area of the path progressively decreases slightly. ,Thus the outer trough 3 may be of ser'ni-circular cross-section and the inner trough 4 of a cross-section curved to give thedesiredprogressive change of area. A continuation from the outer ends of the two trough members and 4 is formed by a second straight annulardifiuser bounded by Walls 5 and 6 concentric with the diffuser a, This difiuser c is connected to and dischargessubstantially radially into a toroidal duct d formed by walls 7 and 3 disposed around the axis of the unit. Aftone position this toroidal duct d merges into afinal outlet pipe 9 which is flanged for receiving a connecting conduit extending at right angles to the axis of the unit. Ihe toroidal duct d is of circular cross-section with area which increases progressively up to the said position fr om each side thereof, from a position diametrically opposite, to accommodate the gas entering all around the annular inletfrom the diffuser 0, without appreciable diflusion. it, The unit is split along a diameter of the toroidal duct d parallel to the axis of the unit, theinner and outer walls 8 and 7 thus meeting by the engagement of flanges 8a and 7a disposed around the axis. Each of the cylindrical flanges 7a and 8a may have its inside surface machined for engaging the other. The semicylindrical part of outer wall 7 carries and merges into the said flanged pipe 3 by merging into twosmoothly curved portions for directing the two streams smoothly intothe final outlet pipe 9. A sufficiently gas-tight joint may be formed by the contact between the two halves of the unit at the flanges 7a andSa. Some fitting bolts 10 with nuts may however be provided around, the flanges to tie together and relatively locate the two halves of the unit. In order that the dimensions of, the bend b shall be sufi'iciently accurate the interior of thewall 3, the outer face of flange 1a and the inner face of flange 7a may be machined in one operation, the opposed face of wall 4 and the outer faces of flanges 8a and 2a being liliewisemachined in one operation; the flanges 1a and 2a can then beatcurately aligned and held together by temporary attachment to a support by bolts through the holes 1b andZ b.

wan the holes for the fitting bolts 10 are rilled through flanges 7a and 8a. If, in use, the unit b nausea to some other ducte. g. a turbine outletonly by the flange 2a, for example, then the bolts 10 relatively locate the two halves of the unit. Alternatively, the flanges 1a and 2a can be both accurately faced against other flanges to which they are bolted through holes 1b and 2b, with packing inserted if necessary, after which the bolts 1% may if desired be removed to leave slight freedom for expansion of the unit without distortion. Alternatively or additionally the unit may be divided along radii thereof into two or more arcuate divisions flanged and bolted together.

Figure 1 shows how the unit may be bolted to the annular outlet from a turbine 11 by bolts and nuts 12.

Iclaim:

1. A diffusing and direction-changing duct unit for fluid, having an annular difiuser duct portion with radially spaced inner ,and outer walls arranged circularly about an axis to define an axially extending diffuser annulus, said walls beingstraight in the axial direction, a toroidal duct portion connected to the diffuser and disposed around the diffuser axis, and a pipe extending from the toroidal duct transversely to the difiuser axis, wherein the diffuser discharges into the toroidal duct substantially along a radius of the toroid and'wherein the toroidal duct is of varying cross-section around its circumference and substantially non-diltusing.

2. A diffusing and direction-changing duct unit for fluid, having an annular difliuser duct portion with radially spaced inner and outer Walls arranged circularly about an axis to define an axially extending difiuser annulus, a toroidal duct portion disposed around the outside of the difiuser, an annular connection from the diflFuser to an annular inlet around the toroidal duct, which connection has at least in part the section of a substantially attaching to the outlet from an elastic fluid turbine, consisting of radially spaced inner and outer walls arranged circularly about an axis to form an axially extending annular diifuser, an annular and substantially non-difiusing connection extending therefrom and curved outwardly through approximately 180 to reverse-the direction of fluid flow, a continuation of said connection constituting a second annular difiuser disposed around and directed oppositely from the first, a toroidal duct disposed around the first annular diffuser with an annular inlet into which the said second difiuser discharges substantially along a radius of the toroid, and a pipe outlet from the toroid, extending substantially radially outwardly from the am's of the first diffuser, the toroid having a minimum diameter diametrically opposite to the outlet pipe and so progressively enlarging towards the pipe as to be substantially non-diffusing.

*4- A diffusing and direction-changing duct unit for fluid, having an annular diifuser duct portion with radially spaced inner and outer walls arranged circularly about an axis to define an axially extending difiuser annulus, said walls being straight in the axial direction, a toroidal duct portion disposed around the ditfuser axis, a pipe extending transversely to the said axis and connctions between said difiuser portion and said toroidal portion and between the latter and said pipe, wherein said toroidal duct and all direction-changing parts of said connections are substantially non-difiusing.

5. A diffusing and direction-changing duct unit for fluid, having a first'duct portion which includes an annular difiuser with radially spaced inner and outer walls arranged circularly about an axis to define an axially extending diffuser annulus, said walls being straight in the axial direction, a toroidal duct portion connected to the said first duct portion and disposed around the diffuser axis, and an outlet pipe extending from the toroidal duct transversely to the difiuser axis, wherein the said first duct portion opens into the toroidal duct at the periphery of the latter and substantially along a radius of the toroid.

6. A duct unit according to claim 5 wherein the said first duct portion includes an annular connection from the diffuser to an annular inlet around the periphery of the toroidal duct portion, which connection has at least in part the section of a substantially pipe bend, the toroidal duct portion being disposed around the outside of the diffuser.

7. A duct unit according to claim 6 wherein the said annular connection is of substantially non-difiusing form around the 180 bend.

8. A duct unit according to claim 7 including a straight duct portion of said annular connection which extends from the said 180 pipe bend along a radius of the toroid up to the peripheral inlet to the toroidal duct portion, which said straight portion is shaped to constitute a second annular difiuser.

9. A diffusing and direction-changing duct unit for fluid having a first duct portion which includes an annular difiuser with radially spaced inner and outer walls arranged circularly about an axis to define an axially extending diffuser annulus and a non-difiusing transfer section connected to said diffuser and curved radially toutwards from said axis, a toroidal duct portion connected to said first duct portion and disposed around said axis, and an outlet pipe extending from the toroidal duct transversely to said axis, wherein the first duct portion opens into the toroidal duct portion at the periphery of the latter and substantially along a radius of the toroid.

10. A diffusing and direction changing duct unit for,

fluid having a first duct portion which includes an annular diffuser with radially spaced inner and outer walls arranged circularly about an axis to define an axially extending diffuser annulus and a non-diffusing transfer section connected to said diiruser and curved radially outwards from said axis, a toroidal duct portion connected to said first duct portion and disposed around said axis, and an outlet pipe extending from the toroidal duct transversely to said axis, wherein the first duct portion opens into the toroidal duct portion substantially along a radius of the toroid and the toroidal duct is of varying cross section around its circumference and substantially nondifiusing.

References Cited in the file of this patent UNITED STATES PATENTS 

